From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sheng Yang Subject: Re: Make QEmu HPET disabled by default for KVM? Date: Thu, 11 Mar 2010 16:38:48 +0800 Message-ID: <201003111638.48661.sheng@linux.intel.com> References: <201003111552.54293.sheng@linux.intel.com> <4B98A99C.8020909@redhat.com> <20100311083157.GZ16909@redhat.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Cc: Avi Kivity , Marcelo Tosatti , kvm@vger.kernel.org To: Gleb Natapov Return-path: Received: from mga06.intel.com ([134.134.136.21]:26310 "EHLO orsmga101.jf.intel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750759Ab0CKIhR (ORCPT ); Thu, 11 Mar 2010 03:37:17 -0500 In-Reply-To: <20100311083157.GZ16909@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Thursday 11 March 2010 16:31:57 Gleb Natapov wrote: > On Thu, Mar 11, 2010 at 10:28:12AM +0200, Avi Kivity wrote: > > On 03/11/2010 10:23 AM, Sheng Yang wrote: > > >>>I have kept --no-hpet in my setup for > > >>>months... > > >> > > >>Any details about the problems? HPET is important to some guests. > > > > > >Seems like HPET reaction is too slow to satisfy some guests(for it would > > >replace PIT). > > > > > >Here is the thread last time. > > > > > >http://thread.gmane.org/gmane.comp.emulators.kvm.devel/44899 > > > > Thanks. We can address this in three ways: first, adjust the guest > > not to do timing related tests when virtualized (since no matter > > what we do, the tests may fail). Second, I think we should > > implement userspace ack notifiers (similar to tpr access notifiers > > already present). Third, we can implement a kernel hpet, which, > > after we solve the zillion bug it introduces, will also give a nice > > performance improvement for hpet intensive workloads. > > Second will not solve the problem. Presence of ack notifiers will not > make HPET interrupt arrive faster. The slow may also due to lost tick. And with the lost tick, hpet is still unusable... -- regards Yang, Sheng